Hi,
No it is not possible to do so.
The best solution I see if you really want to perform such kind of sorting on "product_manufacturer_id" is switch manufacturers.
Using mass action, you can change all products for the manufacturer "X" to the manufacturer "Y".
So, you can move manufacturer X to "1", then manufacturer Y to X and finally, "1" to manufacturer X.
Regards,
Jerome - Obsidev.com
HikaMarket & HikaSerial developer / HikaShop core dev team.
Also helping the HikaShop support team when having some time or couldn't sleep.
By the way, do not send me private message, use the "contact us" form instead.